1. Field of the Invention
The present invention relates to a telephoto lens system capable of closeup shooting that features an aperture ratio of about 1:2.8 and a viewing angle of about 24.4.degree. which ensures high performance over the full shooting distance ranging from the imaging of an infinitely distanct object to a life-size shot.
2. Background of the Invention
Micro or macro lenses have been chiefly used for shooting objects at a near distance. Since most of these lenses are designed to provide best focusing in near-distance shooting, they are not capable of achieving as good aberrational correction when shooting an object at infinity as normal imaging lenses. In response to this situation, a certain type of lens has been proposed that employs a floating mechanism which is capable of correcting the aberrational changes that occur as a result of variation in the shooting distance. Some of the lenses that employ such a floating mechanism have aperture ratios of about 1:2.8 but their focal length is comparatively short (e,g., about 50 mm on a 35 mm camera). In addition, the magnification that can be attained by this lens alone in shooting at the closest focusing distance is approximately 0.5, so that an adapter such as a closeup ring is necessary when shooting the object at a magnification of unity (life size) with this lens. A lens that is capable of near-distance shooting without employing a floating mechanism is also known but because of limitations on its performance this lens can not be made brighter than an aperture ratio of about 1:3.5 to 1:4. In addition, most of the lenses of this type feature magnifications of 0.25-0.5 at the closest focusing distance.
A macro lens that is capable of closeup shooting and which features a focal length of approximately 100 mm in terms of a lens on a 35 mm camera is also known. However, the long focal length of this lens requires a longer lens extension and it is very difficult to produce a system that is capable of shooting at a magnification of unity with this lens alone. Therefore, in order to effect proper focusing when shooting over a very wide range of distances from infinity to a life-size shot, an accessory such as a closeup ring must be used as an aid to permit the lens to be displaced by a distance equal to its focal length.